On direct view HDTVs how does the resolution, or the number of lines change when going from one format to another. For example if you have a 4x3 set and the program is 16x9 with 1080 lines, what is the number of horizontal lines that the set can display? I would thing that it would be something less than 1080.

Most HD-ready 4:3 direct views have a shadow mask with about 600 holes top to bottom, i.e., will support a maximum of about 600 horizontal lines top to bottom. A 16:9 area within the 4:3 area will obviously use only a subset of those lines. That's a far cry from 1080 lines.

Basically, HD-ready 4:3 consumer sets are not very "HD" in the vertical resolution. They're a little better in the horizontal direction.